Display system

ABSTRACT

A display system according to the present invention includes: a dimming device capable of switchably presenting a light reflecting state or a light transmitting state; and a display device for displaying information by modulating light transmitted through the dimming device and/or light reflected by the dimming device. The dimming device has a plurality of regions each being independently capable of switchably presenting a light reflecting state or a light transmitting state, and, when a plurality of types of information are being displayed on the display device, the dimming device is capable of selectively switching between the light reflecting state or the light transmitting state of each of the plurality of regions in accordance with the types of information being displayed.

BACKROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display system, and particularly to adisplay system capable of displaying under a transmission mode usingtransmitted light and displaying under a reflection mode using reflectedlight.

2. Description of the Related Art

In recent years, liquid crystal display devices of reflection types arewidely used as display devices of electronic devices for mobilepurposes. A liquid crystal display device of a reflection type performsdisplay by reflecting ambient light (external light), and thereforeexcels in terms of low power consumption, and is very suitable foroutdoor displaying.

However, a mobile phone or a PDA (mobile information terminal) is put toa very wide range of uses, from outdoor to indoor, or from daytime tonighttime. Therefore, if a reflection type liquid crystal display deviceis employed, the mobile phone or PDA cannot be used in a situation wherethe ambient light is weak. Thus, there is a need for a display devicewhich is capable of performing display regardless of whether the ambientlight is strong or weak.

As such a display device, Japanese Laid-Open Patent Publication No.11-316382 proposes a liquid crystal display device of atransmission/reflection dual-use type (hereinafter also referred tosimply as “dual-use type”), such that a region in which light isreflected and a region in which light is transmitted are created withineach pixel. In the region where light is reflected, this liquid crystaldisplay device performs display under a reflection mode utilizingambient light, and in the region where light is transmitted, performsdisplay in a transmission mode utilizing light from a backlight. Hence,it is possible to perform display regardless of whether the ambientlight is strong or weak. Therefore, such dual-use type liquid crystaldisplay devices are mounted on mobile phones today, and are widely used.

However, in the conventional dual-use type liquid crystal display deviceproposed in Japanese Laid-Open Patent Publication No. 11-316382, supra,each pixel is divided into two regions which utilize light in differentmanners. Therefore, neither during display under the reflection mode norduring display under the transmission mode can a single entire pixelcontribute to displaying. As a result, the display characteristics arenot sufficient as compared to a conventional reflection-type liquidcrystal display device or transmission-type liquid crystal displaydevice in which each entire pixel contributes to displaying. In otherwords, when performing display under the transmission mode, the regionthrough which light is transmitted is narrow and the aperture ratio issmall, so that it is difficult to secure sufficient brightness; on theother hand, when performing display under the reflection mode, theregion which reflects light is narrow, so that it is difficult to securesufficient brightness. Moreover, in the light transmitting region duringdisplay under the reflection mode and in the light reflecting regionduring display under the transmission mode, the retardation of theliquid crystal layer is not optimized, thus allowing light leakage tooccur and increasing the luminance in the black displaying state. Thisleads to a problem of a lowered contrast ratio.

Due to the prevalence of the Internet in the recent years, the contentsto be displayed on a display of an electronic device for mobile purposesmay be various, i.e., not only simple text information, but also stillimages such as photographs and pictures, as well as moving pictures. Theinventor of the present invention has studied the relationship betweenthe type of displayed content and the display mode. As a result, it wasfound that, when displaying text information or still images, displayingunder the reflection mode is preferable from the standpoint of visualrecognition, and when displaying moving pictures, displaying under thetransmission mode is preferable from the standpoint of regardingvividness and luminance as important. However, in a conventionaldual-use type liquid crystal display device, even if displaying underthe reflection mode and displaying under the transmission mode areswitched in accordance with the content to be displayed, the displaycharacteristics will not be sufficient, as already described above.

Furthermore, due to diversification of the contents to be displayed, itis expected that different types of information will frequently bedisplayed simultaneously within a display region of a display device(e.g., moving pictures and text information). However, with aconventional dual-use type liquid crystal display device, it isimpossible to perform display under the transmission mode in a partialregion within the display region while performing display under thereflection mode in the other region.

Thus, to date, no display device which exhibits sufficient displaycharacteristics in a multitude of scenes, or no display device which issuitable for the displaying of multiple contents, has been developed.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problems, and amain purpose thereof is to provide a display system which has gooddisplay characteristics during both display under the transmission modeand display under the reflection mode, and which is suitable for use ina multitude of scenes and/or displaying of multiple contents.

A display system according to the present invention is a display systemcomprising: a dimming device capable of switchably presenting a lightreflecting state or a light transmitting state; and a display device fordisplaying information by modulating light transmitted through thedimming device and/or light reflected by the dimming device, wherein thedimming device has a plurality of regions each being independentlycapable of switchably presenting a light reflecting state or a lighttransmitting state, and, when a plurality of types of information arebeing displayed on the display device, the dimming device is capable ofselectively switching between the light reflecting state or the lighttransmitting state of each of the plurality of regions in accordancewith the types of information being displayed.

In a preferred embodiment, the display device supplies a display signalto a first display region for performing display by modulating the lighttransmitted through the dimming device, and supplies a display signal toa second display region for performing display by modulating the lightreflected by the dimming device, the display signals being of differenttypes.

In a preferred embodiment, the display device has a plurality of pixels;and each of the plurality of regions of the dimming device correspondsto each of the plurality of pixels in a one-to-one relationship.

In a preferred embodiment, the dimming device is a dimming device havinga layered structure including a first layer and a second layer, suchthat a light reflectance of the first layer changes in response to anexternal stimulation; the first layer contains a first material whoseoptical characteristics change in accordance with a concentration of aspecific element; and the second layer contains a second materialcapable of containing the specific element, the second materialreleasing or absorbing the specific element in accordance with theexternal stimulation.

In a preferred embodiment, the dimming device is a dimming devicecomprising a dimming layer whose light reflectance changes in responseto an external stimulation; and the dimming layer contains a firstmaterial whose optical characteristics change in accordance with aconcentration of a specific element, the first material being particles.

Alternatively, a display system according to the present invention is adisplay system comprising: a dimming device capable of switchablypresenting a light reflecting state or a light transmitting state; and adisplay device for performing display by modulating incident light,wherein, the dimming device is a dimming device having a layeredstructure including a first layer and a second layer, such that a lightreflectance of the first layer changes in response to an externalstimulation; the first layer contains a first material whose opticalcharacteristics change in accordance with a concentration of a specificelement; and the second layer contains a second material capable ofcontaining the specific element, the second material releasing orabsorbing the specific element in accordance with the externalstimulation.

Typically, the display device performs display by modulating lighttransmitted through the dimming device and/or light reflected by thedimming device.

In a preferred embodiment, the element is hydrogen, and the firstmaterial is able to transition between a light reflecting state and alight transmitting state in accordance with a hydrogen concentration.

In a preferred embodiment, the second layer contains a hydrogen storagematerial.

In a preferred embodiment, operation occurs in a region where respectivehydrogen equilibrium pressure-composition isotherms (PTC characteristiccurves) of the first layer and the second layer are substantially flat.

In a preferred embodiment, in the region where the PTC characteristiccurves are substantially flat, hydrogen equilibrium pressures of thefirst layer and the second layer are about the same.

In a preferred embodiment, a range of hydrogen storage amount of thesecond layer in the region where the PTC characteristic curve issubstantially flat encompasses a range of hydrogen storage amount of thefirst layer in the region where the PTC characteristic curve issubstantially flat.

In a preferred embodiment, the second material releases or absorbs thespecific element through exchanges of electrons.

In a preferred embodiment, the second material releases or absorbs thespecific element in response to light irradiation.

In a preferred embodiment, the second layer contains a material having aphotocatalytic ability.

In a preferred embodiment, a pair of conductive layers for forming anelectric field for causing ions of the specific element to move from thesecond material to the first material, or from the first material to thesecond material, are comprised.

In a preferred embodiment, the first and second layer are positionedbetween the pair of conductive layers.

In a preferred embodiment, the first layer has conductivity, andfunctions as one of the pair of conductive layers.

In a preferred embodiment, the second layer has conductivity, andfunctions as one of the pair of conductive layers.

In a preferred embodiment, the second layer has a light transmittingability.

In a preferred embodiment, at least one of the first layer and thesecond layer has a multi-layer structure.

Alternatively, a display system according to the present invention is adisplay system comprising: a dimming device capable of switchablypresenting a light reflecting state or a light transmitting state; and adisplay device for performing display by modulating incident light,wherein, the dimming device is a dimming device comprising a dimminglayer whose light reflectance changes in response to an externalstimulation; and the dimming layer contains a first material whoseoptical characteristics change in accordance with a concentration of aspecific element, the first material being particles.

Typically, the display device performs display by modulating lighttransmitted through the dimming device and/or light reflected by thedimming device.

In a preferred embodiment, the first material is able to transitionbetween a light reflecting state and a light transmitting state inaccordance with the concentration of the specific element.

In a preferred embodiment, the dimming layer diffuse-reflects light whenthe first material is in the light reflecting state.

In a preferred embodiment, a diameter of the particles is equal to orgreater than 350 nm and equal to or less than a thickness of the dimminglayer.

In a preferred embodiment, the specific element is hydrogen.

In a preferred embodiment, a conversion layer containing a secondmaterial capable of containing the specific element is furthercomprised, wherein the second material releases or absorbs the specificelement in accordance with the external stimulation.

In a preferred embodiment, the specific element is hydrogen, and theconversion layer contains a hydrogen storage material.

In a preferred embodiment, operation occurs in a region where respectivehydrogen equilibrium pressure-composition isotherms (PTC characteristiccurves) of the dimming layer and the conversion layer are substantiallyflat.

In a preferred embodiment, in the region where the PTC characteristiccurves are substantially flat, hydrogen equilibrium pressures of thedimming layer and the conversion layer are about the same.

In a preferred embodiment, a range of hydrogen storage amount of theconversion layer in the region where the PTC characteristic curve issubstantially flat encompasses a range of hydrogen storage amount of thedimming layer in the region where the PTC characteristic curve issubstantially flat.

In a preferred embodiment, the second material releases or absorbs thespecific element through exchanges of electrons.

In a preferred embodiment, the second material releases or absorbs thespecific element through an electrochemical reaction.

In a preferred embodiment, a pair of conductive layers for forming anelectric field for causing ions of the specific element to move from thesecond material to the first material, or from the first material to thesecond material, are comprised.

In a preferred embodiment, the dimming layer and the conversion layerare positioned between the pair of conductive layers.

In a preferred embodiment, the dimming layer has conductivity, andfunctions as one of the pair of conductive layers.

In a preferred embodiment, the conversion layer has conductivity, andfunctions as one of the pair of conductive layers.

In a preferred embodiment, the conversion layer has a light transmittingability.

In a preferred embodiment, at least one of the dimming layer and theconversion layer has a multi-layer structure.

In a preferred embodiment, the display device is a liquid crystaldisplay device including a pair of substrates and a liquid crystal layerprovided between the pair of substrates.

In a preferred embodiment, an illumination device disposed on anopposite side from a viewer with respect to the display device isfurther comprised.

In a preferred embodiment, the dimming device is disposed between thedisplay device and the illumination device.

In a preferred embodiment, the dimming device is disposed inside thedisplay device.

In a preferred embodiment, the display device includes a first colorfilter.

In a preferred embodiment, the dimming device includes a second colorfilter.

In a preferred embodiment, the display device includes a first colorfilter; the dimming device includes a second color filter; and thesecond color filter is disposed on an opposite side from a viewer withrespect to the first layer.

In a preferred embodiment, the display device includes a first colorfilter; the dimming device includes a second color filter; and thesecond color filter is disposed on an opposite side from a viewer withrespect to the dimming layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing a display systemaccording to the present invention.

FIG. 2 is a diagram schematically showing how display modes are switchedin accordance with content types.

FIG. 3 is a schematic diagram showing a manner in which display modesare switched.

FIG. 4 is a schematic diagram showing a manner in which display modesare switched.

FIG. 5 is a cross-sectional view schematically showing the constitutionof a dimming device.

FIGS. 6(a), (b), and (c) are diagrams illustrating operation principlesof the dimming device shown in FIG. 5.

FIG. 7 is a cross-sectional view schematically showing a dimming device.

FIG. 8 is a graph showing a hydrogen equilibrium pressure-compositionisotherm (PTC characteristic curve) of a dimming layer and a conversionlayer.

FIG. 9 is a diagram showing the operation of another dimming device.

FIG. 10 is a cross-sectional view schematically showing another dimmingdevice.

FIG. 11 is a cross-sectional view schematically showing another dimmingdevice.

FIG. 12 is a cross-sectional view schematically showing another dimmingdevice.

FIG. 13 is a cross-sectional view schematically showing another dimmingdevice.

FIG. 14 is a cross-sectional view showing a first embodiment of thedisplay system according to the present invention.

FIG. 15 is a cross-sectional view showing a second embodiment of thedisplay system according to the present invention.

FIG. 16 is a cross-sectional view showing a third embodiment of thedisplay system according to the present invention.

FIG. 17 is a cross-sectional view showing a third embodiment of thedisplay system according to the present invention.

FIG. 18 is a cross-sectional view showing a third embodiment of thedisplay system according to the present invention.

FIG. 19 is a cross-sectional view showing a fourth embodiment of thedisplay system according to the present invention.

FIG. 20 is a cross-sectional view schematically showing the constitutionof a dimming device containing dimming particles.

FIG. 21 is a cross-sectional view schematically showing a dimming devicecontaining dimming particles.

FIGS. 22(a) and (b) are cross-sectional views schematically showingother dimming devices containing dimming particles.

FIG. 23 is a cross-sectional view schematically showing another dimmingdevice containing dimming particles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, with reference to the figures, embodiments of the presentinvention will be described. Note that the present invention is not tobe limited to the embodiments below.

First, with reference to FIG. 1, the fundamental constitution of adisplay system 100 according to the present invention will be described.

The display system 100 comprises a dimming device 10 which is capable ofswitchably presenting a light reflecting state or a light transmittingstate, and a display device 20 which performs display by modulatingincident light. The display system 100 further comprises a backlight(illumination device) 30 which is disposed at the rear face side (i.e.,the opposite side from the viewer) of the display device 20.

The dimming device 10, which is a device capable of switchablypresenting a state of reflecting light or a state of transmitting light,is disposed between the display device 20 and the backlight 30. As shownin FIG. 1, the dimming device 10 of the present embodiment has a layeredstructure including the dimming layer 1 and the conversion layer 2, andthe light reflectance of the dimming layer 1 changes responsive toelectrical stimulations. The dimming device 10 further comprises a pairof electrodes 3 a and 3 b, between which the dimming layer 1 and theconversion layer 2 are interposed. The more detailed constitution andoperation principles of the dimming device 10 will be described later.

The display device 20 is able to modulate both the light which entersfrom its front face side and the light which enters from its rear face,and displays information by modulating the light which has beentransmitted through the dimming device 10 and/or the light which hasbeen reflected by the dimming device 10. For example, the display device20 is a liquid crystal display device having a pair of substrates and aliquid crystal layer interposed between these substrates, and controlsthe orientation state of the liquid crystal layer by applying a voltageto transparent electrodes which are provided on the surfaces of the pairof substrates facing the liquid crystal layer, thus modulating the lighttraveling through the liquid crystal layer. Note that the display device20 is not limited to a liquid crystal display device. Any display devicemay be used that is capable of modulating light which enters from thefront face side as well as light which enters from the rear face.

As shown on the left-hand side of FIG. 1, when the dimming device 10 isin a light transmitting state, if the backlight 30 is activated (ONstate), light from the illumination device 30 is transmitted through thedimming device 10 and enters the display device 20. Therefore, bymodulating this incident light at the display device 20, the displaysystem 100 is able to perform display under the transmission mode.

On the other hand, as shown on the right-hand side of FIG. 1, when thedimming device 10 is in a light reflecting state, light entering thedisplay device 20 from the front face side travels through the displaydevice 20 and thereafter is reflected by the dimming device 10, andagain travels through the display device 20. Therefore, by modulatinglight during this process, the display system 100 is able to performdisplay under the reflection mode. At this time, the backlight 30 may bedeactivated (OFF state) in synchronization with the switching of thedimming device 10 to a light reflecting state, or may be left activated(ON state). If the backlight 30 remains activated, the light from theillumination device 30 is reflected at the dimming device 10, andtherefore hardly enters the display device 20.

Thus, the display system 100 is able to switchably perform display underthe reflection mode or display under the transmission mode, and thedisplay device 20 can be allowed to function as either a reflection typedisplay device or as a transmission type display device. Since each ofthe plurality of pixels of the display device 20 does not need to bedivided into a region for reflecting light and a region for transmittinglight, each entire pixel can contribute to displaying either duringdisplay under the reflection mode or during display under thetransmission mode in the display system 100. Therefore, as compared to aconventional liquid crystal display apparatus of atransmission/reflection dual-use type such as that disclosed in PatentDocument 1, a bright and high-contrast ratio display can be realized inboth the reflection mode and the transmission mode. Therefore, thedisplay system 100 of the present invention can be suitably used invarious situations, i.e., in a multitude of scenes.

It is preferable that the dimming device 10 has a plurality of regions(referred to as “dimming regions”) each of which is independently ableto switchably present a light reflecting state or a light transmittingstate, and it is preferable that, when a plurality of types ofinformation are displayed on the display device 20, the light reflectingstate or light transmitting state of each dimming region is selectivelyswitched in accordance with the type of information. With such aconstitution, when different types of contents are displayed on thedisplay device 10, as shown in FIG. 2, display can be performed in amode which provides optimum visual recognition depending on each contenttype, so that the display system 100 can be suitably used for displayingmultiple contents. Note that, although FIG. 2 illustrates an examplewhere display under the reflection mode is performed in a region wheretext information is displayed and display under the transmission mode isperformed in regions where moving picture information and still imageinformation are displayed, the correspondence between contents anddisplay modes is not limited thereto. For example, from the standpointof being easy on the eyes, display under the reflection mode may beperformed in a region where still image information is displayed.

In the case of the dimming device 10 of the present embodiment, forexample, the electrodes 3 a and 3 b sandwiching the dimming layer 1 andthe conversion layer 2 may be patterned into predetermined shapes,whereby it becomes possible to independently apply electricalstimulations to a plurality of sites in the dimming layer 1, thusrealizing a plurality of dimming regions.

The number, size, positioning, etc., of the dimming regions may beappropriately determined based on the purpose and the like of thedisplay system 100.

For example, as shown in FIG. 3, the dimming device 10 may be dividedrelatively roughly, and the size of each content to be displayed in adisplay region 20 r (size of each region to be displayed) may be adaptedto the size of a dimming region 10 r.

Alternatively, as shown in FIG. 4, the dimming device 10 may be dividedinto sizes substantially the same as those of the pixels of the displaydevice 20, and each dimming region 10 r may be switched between thelight transmitting state and the light reflecting state, in accordancewith the size of a content to be displayed in the display region 20 r.

In FIG. 4, dimming regions 10 r are defined at the intersections betweenelectrodes 3 a and 3 b, which are patterned in stripes havingsubstantially the same pitch as a pixel pitch of the display device 20,each dimming region 10 r corresponding to each pixel of the displaydevice 20 in a one-to-one relationship. First, content information to bedisplayed is converted by a display signal conversion controller 21 intoa signal for displaying. Next, when sending a signal to a display devicedriving circuit (display device driver) 22 for driving the displaydevice 20, a synchronized signal is also sent to a dimming devicedriving circuit (dimming device driver) 12 for driving the dimmingdevice 10, whereby it becomes possible to selectively switch between thelight reflecting state and the light transmitting state of each dimmingregion of the dimming device 10 in accordance with the type of thecontent displayed by the display device 20.

Note that, displaying under the reflection mode (which is easy on theeye) is often preferable when displaying text information or still imageinformation, from the standpoint of visual recognition; and displayingunder the transmission mode is often preferable when displaying movingpicture information, from the standpoint of regarding vividness andluminance as important. However, since differences in visual recognitionand differences in preferences concerning images may exist for eachviewer, it is more preferable to permit the display mode to be manuallyswitchable.

(Dimming Device)

Hereinafter, the constitution and operation principles of the dimmingdevice 10 according to the present embodiment will be described. Priorto that, a technique which has conventionally been proposed as a dimmingmirror will be described.

A phenomenon in which a metal thin film of yttrium (Y), lanthanum (La),or the like binds to hydrogen to change into a hydride which cantransmit visible light has been reported in the specification of U.S.Pat. No. 5,635,729, and Huibert et al. (Nature, March 1996, vol. 380,pp. 231-234). Since this phenomenon is reversible, by adjusting thehydrogen pressure in the atmosphere, it becomes possible to cause thethin film to change between a metallic luster state and a transparentstate.

By changing the optical characteristics of the above thin film so as toswitch between a state exhibiting a metallic luster and a transparentstate, it becomes possible to realize a dimming mirror which is capableof freely adjusting the reflectance/transmittance of light. If a dimmingmirror is used as a windowpane of a building or an automobile, forexample, it becomes possible to shield (reflect) or transmit sunlight asnecessary.

Such a dimming mirror has, for example, a structure in which a palladiumlayer is formed on a yttrium thin film. The palladium has a function ofpreventing surface oxidation of the yttrium thin film, and a function ofcausing hydrogen molecules in the atmosphere to be efficiently changedinto hydrogen atoms so as to be supplied to yttrium. When yttriumchemically binds to hydrogen atoms, either YH₂ or YH₃ is formed. WhileYH₂ is a metal, YH₃ is a semiconductor and has a forbidden band widthwhich is greater than the energy of visible light, and therefore istransparent.

Moreover, since changes of states between YH₂

YH₃ occur rapidly (about several seconds) even at room temperature, itis possible to perform switching between a reflection (metallic luster)state and a transparent state depending on the amount of hydrogencontent in the atmosphere.

As another material which is capable of such transitioning betweenmetallic luster

transparent, a Mg₂Ni thin film is disclosed in Japan Society of AppliedPhysics, 2001 Spring Meeting, 31-a-ZS-14, for example.

Although the above conventional techniques can cause changes in theoptical state of a thin film, it would be difficult to practicallyrealize a dimming device by using the described constitutions. For one,it is necessary to expose the thin film to an hydrogen atmosphere.Specifically, it is necessary to control the amount of hydrogen(hydrogen partial pressure) in an atmosphere gas which is in contactwith the thin film. Therefore, it is difficult to realize a practicaldimming device by using the aforementioned conventional constitution.

Hereinafter, the dimming device 10 according to the present embodimentwill be described.

First, the fundamental constitution of the dimming device 10 will bedescribed with reference to FIG. 5. As shown in FIG. 5, the dimmingdevice 10 has a layered structure including a dimming layer M1 and aconversion layer M2, such that the light reflectance of the dimminglayer M1 changes in response to external stimulations.

The dimming layer M1 contains a dimming material whose opticalcharacteristics change in accordance with the concentration of aspecific element. Preferable examples of the dimming material are Y, La,and Mg₂Ni alloy as described above. Materials such as Y, La, and Mg₂Nalloy undergo transitions between metal and semiconductor (or insulator)states in accordance with hydrogen concentration.

The conversion layer M2 contains a material capable of containing aspecific element such as hydrogen (which in the present specification isreferred to as a “conversion material”). The conversion materialreleases or absorbs the aforementioned specific element (e.g., hydrogen)in accordance with an external stimulation, such as a charge (electronsor holes) injection/release or light irradiation.

Hereinafter, a mechanism where, responsive to injection/release of acharge, hydrogen ions move from the conversion layer M2 to the dimminglayer M1, or from the dimming layer M1 to the conversion layer M2, willbe described. A characteristic feature of this mechanism lies in thations of a specific element (hydrogen) which causes a change in theoptical characteristics of the dimming layer M1 are moved, not via anelectrochemical reaction, but by way of a charge movement.

First, FIG. 5 is referred to. The dimming layer M1 and the conversionlayer M2 shown in FIG. 5 both have the ability to absorb/releasehydrogen, and have an electrical conductivity for being able to movecharges (electrons or holes) and ions.

Next, FIG. 6(a) is referred to. FIG. 6(a) shows an initial state of thedimming layer M1 and the conversion layer M2 included in the structureof FIG. 5. In this initial state, an equilibrium state is establishedbetween the dimming layer M1, which substantially stores no hydrogen,and the conversion layer M2, which has hydrogen stored in advance. Sincethe dimming layer M1 lacks a sufficient concentration of hydrogen, thedimming layer M1 is in a metallic state, thus exhibiting metallicluster.

Next, as shown in FIG. 6(b), a negative potential is applied to thedimming layer M1 side, while a positive potential is applied to theconversion layer M2 side. At this time, electrons are injected to thedimming layer M1 from a negative electrode (not shown), so that thedimming layer M1 enters an electron-rich state. On the other hand, holesare injected to (i.e., electrons are withdrawn from) the conversionlayer M2. The holes which have been injected to the conversion layer M2move inside the conversion layer M2 toward the dimming layer M1. Duringsuch movements of the holes, if further holes continue to be injected tothe conversion layer M2, the conversion layer M2 enters a hole-richstate. As a result, the conversion layer M2 enters a state wherehydrogen ions are likely to be released, whereas in the dimming layerM1, the amount of hydrogen ions which are received from the conversionlayer M2 and retained therein increases.

Therefore, the hydrogen equilibrium state which existed between thedimming layer M1 and the conversion layer M2 is broken, so that thedimming layer M1 takes a state where more hydrogen is likely to beretained, and thus the hydrogen ions released from the conversion layerM2 will move to the dimming layer M1. Thus, as shown in FIG. 6(c), a newequilibrium state is established. In this state, the hydrogen which hasmoved to the dimming layer M1 binds to the dimming material, whereby thedimming layer M1 becomes transparent.

The above reaction can be described as M1+M2(H)→M1(H)+M2. Herein, M1(H)and M2(H) respectively represent a state where hydrogen is retained inthe dimming layer M1 and a state where hydrogen is retained in theconversion layer M2.

As is clear from the above explanation, only hydrogen ion exchanges takeplace between the dimming layer M1 and the conversion layer M2, and noother reactions involving ions are taking place. Moreover, when thepolarities of the applied voltages are inverted from the state of FIG.6(c), a reaction will progress in the opposite direction, thus returningto the original equilibrium state shown in FIG. 6(a).

Thus, according to the present invention, it is possible to drivehydrogen by causing the hydrogen equilibrium state to be changed basedon movements of charges (electrons or holes). Therefore, it isunnecessary to involve any ions other than hydrogen ions in thereaction. As a result, the response speed becomes faster than in anyelectrochemical reaction that involves a plurality of kinds of ions.Moreover, since no electrochemical reaction occurs, there is littlepossibility for hydrogen gas to be generated at the positive side, sothat a stable operation is enabled as an electronic device.

Hereinafter, the more specific constitution of the dimming device 10will be described.

The dimming device shown in FIG. 7 has a layered structure including adimming layer 1 and a conversion layer 2, such that the lightreflectance (optical characteristics) of the dimming layer 1 changes inresponse to electrical stimulations. This dimming device comprises apair of electrodes 3 a, 3 b sandwiching the dimming layer 1 and theconversion layer 2, and a substrate 4 supporting the layered structure.An appropriate voltage is to be externally applied to the pair ofelectrodes 3 a, 3 b. However, the electrode 3 a and the electrode 3 bmay simply be short-circuited as necessary.

Note that the layering order of the conversion layer 2 and the dimminglayer 1 with respect to the substrate 4 is not limited to that which isillustrated in the figures, but the conversion layer 2 may be disposedso as to be closer to the substrate 4, with the dimming layer 1 beingformed thereupon.

The dimming layer 1 in the present embodiment contains a dimmingmaterial (e.g., yttrium) whose optical characteristics change inaccordance with the hydrogen concentration. The whole or part of thedimming layer 1 may be composed of a single layer or multiple layers ofdimming material. Alternatively, particles of dimming material may bepresent, in a dispersed or linked state, within a film which is composedof another material.

The conversion layer 2 contains a conversion material which is capableof containing hydrogen. This conversion material performs exchanges ofelectrons with the electrode 3 a, thus effecting release/absorption ofhydrogen ions (H⁺).

In the illustrated example, a positive potential is applied to theelectrode 3 a and a negative potential is applied to the electrode 3 b,whereby hydrogen ions are released from the dimming material in theconversion layer 2 containing a sufficient amount of hydrogen inadvance. The released hydrogen ions move within an electric field whichis generated in the layered structure, and reach the dimming layer 1,thus leaving the dimming material doped therewith. Such a mechanism ofhydrogen release and movement is as described above. The dimmingmaterial in the dimming layer 1 binds to hydrogen, thus forming ahydrogen metal compound. As a result, the dimming material, which wasinitially in a metallic state, changes to a semiconductor or insulatorthat transmits visible light.

The dimming layer 1 may be produced by a vapor deposition technique, asputtering technique, or the like. In the case where the dimming layer 1is to function as a mirror exhibiting a metallic luster, the dimminglayer 1 is preferably formed from a film which has as good a planarityas possible.

The conversion material contained in the conversion layer 2 is able tostore and retain atoms or ions of hydrogen in its stationary state, andchanges its hydrogen storage amount (retained amount) in accordance withexternal stimulations. As this material capable of storing hydrogen,alloys such as LaNi₅, MnNi₅, CaNi₅, TiMn_(1.5), ZrMn_(1.5), ZrMn₂, TiNi,TiFe, and Mg₂Ni can be used. Moreover, carbon nanotubes (CNT) may alsobe used.

The conversion layer 2 may contain an electrically conductive materialin addition to the hydrogen storage material. If an electricallyconductive material is contained in the conversion layer 2, it ispossible to rapidly perform exchanges of hydrogen ions with the dimminglayer 1. As an electrically conductive material, a material capable ofion transmission, such as a liquid or solid electrolyte, or a conductivepolymer or a charge transfer complex which transmits charge (electronsor holes) can be used. Moreover, in addition to the aforementionedhydrogen storage material or electrically conductive material, a bindingmaterial such as a binder resin may be added to the conversion layer 2as necessary. Note that, in order to surely restrain the charge whichhas been injected from one electrode from immediately moving to theother electrode, a separator layer may be inserted between the dimminglayer and the conversion layer. As the material of the separator layer,it is desirable to choose a material which permits ion movement but isunlikely to permit charge movement. For example, an ion exchanger, aporous insulator, an ion conductive polymer material or the like can beused. By disposing a separate layer composed of such a material, thecharge which has been injected from an electrode is surely preventedfrom penetrating to the other electrode, whereby the charge movementefficiency between the dimming layer and the conversion layer can beenhanced.

In the case where the conversion layer 2 is composed of a mixture of aplurality of materials, a solution obtained by dissolving such materialsin a solvent may be prepared and applied by a spin coating technique ora printing technique, whereby the conversion layer 2 can be easilyformed. Such formation of the conversion layer 2 may be performed by anink jet technique or any other thin film deposition technique.

As described above, according to the present embodiment, exchanges ofcharges and ions occur inside the conversion layer 2 responsive toapplication of a voltage to the electrodes 3 a, 3 b. As a result, owingto the aforementioned mechanism, hydrogen movement can be inducedbetween the conversion layer 2 and the dimming layer 1. Therefore, forexample, by using a dimming layer 1 which is undoped with hydrogen in aninitial state and a conversion layer 2 having hydrogen stored inadvance, if a voltage as shown in FIG. 5 is applied, hydrogen ions movefrom the positive side to the negative side, thus making the dimminglayer 1 doped therewith. In other words, a hydrogen release reactionprogresses at the positive side, whereas a combination reaction betweenhydrogen and a metal progresses at the negative side, whereby a hydrogenmetal compound is formed. On the other hand, if a voltage in theopposite direction is applied, a hydrogen movement in the oppositedirection occurs. Therefore, by reversing the polarity of the appliedvoltage, the optical state of the dimming layer 1 can be reversiblyswitched between metallic luster and transparent.

When only contemplating a movement of the hydrogen stored in theconversion layer 2, the electrodes 3 a and the electrodes 3 b might beshort-circuited outside of the layered structure. Such short-circuitingwould be a similar phenomenon to a discharging of a secondary battery,and enable restoration of the internal state of the layered structure tothe initial state.

Since the conversion layer 2 and the dimming layer 1 have the ability toretain hydrogen, when voltage application is not performed (when theexternal circuit is open), no hydrogen movement occurs, so that theoptical state of the dimming layer 1 is retained (memory function of thedimming layer). Therefore, by choosing a material having a good hydrogenretaining ability, it becomes possible to retain a dimmed state for along period of time without consuming power.

Contrary to the above example, a dimming layer 1 doped with hydrogen inadvance, and a conversion layer 2 in a state not storing hydrogen may beused. In that case, hydrogen may be moved from the dimming layer 1 tothe conversion layer 2 by applying a positive potential to the dimminglayer 1 and a negative potential to the conversion layer 2, thus causinga change in the optical state of the dimming material in the dimminglayer 1.

In the present embodiment, the light reflectance/light transmittance ofa dimming material can be controlled based on a doping amount ofhydrogen. Therefore, by controlling the voltage to be applied to theelectrode and application time (e.g., a duty ratio), the lightreflectance/light transmittance of the dimming layer 1 can becontrolled. By utilizing the memory ability based on hydrogen retainingability, an appropriate light reflectance/light transmittance can beeasily retained.

In appropriately controlling such hydrogen storage/release, it isnecessary to pay attention to the hydrogen equilibriumpressure-composition isotherm (hereinafter referred to as a “PTCcharacteristic curve”) As shown in FIG. 8, the PTC characteristic curverepresents a relationship between the stored hydrogen amount and thehydrogen equilibrium pressure. In the graph of FIG. 8, the horizontalaxis represents the hydrogen storage amount, whereas the vertical axisrepresents the hydrogen equilibrium pressure.

In a portion of the PTC characteristic curve that is generally parallelto the horizontal axis (hereinafter referred to as the “plateauregion”), the stored hydrogen amount is capable of changing under aconstant equilibrium pressure, and therefore hydrogen absorption/releasecan be reversibly carried out in a state under a constant hydrogenequilibrium pressure. For this reason, the dimming device of the presentembodiment performs switching operations in the plateau region of thePTC characteristic curve.

It is desirable that the conversion layer 2 and the dimming layer 1exhibit substantially similar PTC characteristics. More specifically, asshown in FIG. 8, it is desirable that the ranges of “hydrogen storageamount” of the plateau regions of the PTC characteristic curves of theconversion layer 2 and the dimming layer 1 overlap each other, and thatthe “hydrogen equilibrium pressure” levels are substantially equal. Byexhibiting similar hydrogen equilibrium pressures, it becomes possibleto smoothly perform hydrogen exchanges between the dimming layer 1 andthe conversion layer 2. The reason is that, if the hydrogen equilibriumpressure difference between the dimming layer 1 and the conversion layer2 becomes large, it will be impossible to perform hydrogen exchangesbetween the two layers even if hydrogen absorption/release occurs ineach layer.

Moreover, it is more preferable that the hydrogen storage amount range(span) of the plateau region of the PTC characteristic curve of theconversion layer 2 is of a size encompassing the hydrogen storage amountrange (span) of the plateau region of the PTC characteristic curve ofthe dimming layer 1. The reason is that, in the dimming device of thepresent embodiment, the light transmittance of the dimming layer 1 iscontrolled by the hydrogen doping amount of the dimming layer 1;therefore, if the extent of change in the hydrogen storage amount of theconversion layer 2 were smaller than the extent of change in thehydrogen doping amount that is necessary for causing a state change ofthe dimming layer 1, the optical state of the dimming layer 1 would notbe sufficiently changed.

FIG. 7 is referred to again. Since the dimming device 10 shown in FIG. 7performs switching between a metallic reflection state and a transparentstate, it is preferable that the entire device has a high transparency.In order to establish a high transparency state, not only the substrate4 and the electrodes 3 a, 3 b but also the conversion layer 2 must beformed from a material which has a high transmittance (no absorption) inthe entire visible light region. However, a conversion material such asa hydrogen storage material is often a metal or a colored material, andit may be difficult to form a conversion layer 2 having a hightransparence from a layer of such a conversion material. Therefore, itis preferable to form the conversion layer 2 by mixing microparticles ofa conversion material with a transparent material. Specifically,nanoparticles having a grain size equal to or less than the lightwavelength are formed from a conversion material, and thesenanoparticles may be bound with a binder resin which has a goodtransparence. A conversion layer 2 thus produced is not only able toexhibit both transparence and hydrogen storing ability, but an increasein the hydrogen absorption/release efficiency can also be expected sincethe conversion material has an increased surface area because of beingmade into nanoparticles. An increase in the hydrogen absorption/releaseefficiency of the conversion material is preferable because the responsespeed of the dimming operation would be improved. As a conversionmaterial in an ultrafine particle state, a carbon type material (e.g.,CNT and fullerene), a potassium-graphite interlayer compound or the likecan also be used.

In order to realize exchanges of charges and ions between the dimminglayer 1 and the conversion layer 2, it is preferable to dispose a filmof conductive polymer material P1 (a material capable of transportingboth charges, i.e., electrons and holes) between the dimming layer 1 andthe conversion layer 2. Instead of disposing a polymer film having acharge moving ability, an electrolyte film may be disposed. By disposingan electrolyte film, movement of hydrogen ions becomes likely to occurvia the electrolyte, and therefore it is possible to improve thecharacteristics. The conductive polymer material P1 is doped with ionsfor conferring conductivity, and therefore also functions as anelectrolyte film. A blend of a conductive polymer material P1 and, as abinder resin, an acrylic resin having about the same refractive index asthat of glass can be used.

The dimming device is not limited to those described above, but permitsvarious modifications. Hereinafter, with reference to FIGS. 9 to 13,other dimming devices 10A to 10D will be described.

The dimming device 10A shown in FIG. 9 and FIG. 10 is capable ofswitching between a metal diffuse reflection (white) state and a lighttransmitting state.

As shown in FIG. 10, the dimming device 10A has a structure in which anelectrode 3 b, a conversion layer 2, a dimming layer 1, and an electrode3 a are layered in this order on a substrate 4 having bumps and dents.In order to effect diffuse-reflection, minute bumps and/or dents arepresent on the surface of the dimming layer 1.

With reference to FIG. 9, the operation of the dimming device 10A ofFIG. 10 will be described.

In FIG. 9, the electrodes 3 a, 3 b are omitted from illustration forsimplicity. Since minute bumps are present on the surface of the dimminglayer 1, light can be diffuse-reflected when the dimming layer 1 is in ametallic reflection state as shown on the left-hand side of FIG. 9. Onthe other hand, when the dimming layer 1 is in a transparent state asshown on the right-hand side of FIG. 9, the conversion layer 2 in theunderlying layer absorbs light.

In the example shown in FIG. 9, the surface of the substrate has minutebumps, and therefore the conversion layer 2 and the dimming layer 1 areof such an overall planarity that the bumps and dents of the substrateare reflected in their shapes. In other words, not only the upper face(the face on the light reflecting side) of the dimming layer 1, but alsothe bottom face has a shape reflecting the underlying bumps and dents.However, it is not necessary for the underlying conversion layer 2 tohave a bump/dent structure. Therefore, minute dents and/or bumps may beformed only on the upper face of the dimming layer 1, while thesubstrate surface and the conversion layer 2 may be formed flat.

Thus, in accordance with the dimming device 10A, while the dimming layer1 is in a metallic reflection state, the reflected light is scatteredand perceived as white, so that the surface of the dimming layer 1appears white.

The dimming device 10A may have a similar constitution to that of thedimming device 10, except that the substrate 4 having bumps and dentsformed on its surface is used. For example, as the conversion layer 2,what is obtained by blending a potassium-graphite interlayer compoundwhich is a hydrogen storage material, a conductive polymer material P1(a material capable of transporting both charges, i.e., electrons andholes), and an acrylic resin serving as a binder resin can be suitablyused.

Next, with reference to FIG. 11, another dimming device 10B will bedescribed.

In dimming device 10B, as shown in FIG. 11, the dimming layer 1 itselfdoubles as one of the electrodes. Since the dimming layer 1 isfundamentally a metal thin film, the dimming layer 1 can function as anelectrode. Since the dimming layer 1 doubles as an electrode, a step offorming an electrode is omitted, whereby the number of production stepsfor the dimming device can be reduced.

Note that, although the dimming device 10B in FIG. 11 is atransparent-metal reflection type dimming device, the dimming layer 1can double as an electrode in a dimming device of any other typedescribed above.

Next, with reference to FIG. 12, another dimming device 10C will bedescribed.

The dimming device 10C has a constitution in which a conversion layer isseparated into a plurality of layers, i.e., a first conversion layer 2a, and a second conversion layer 2 b. In the dimming device of thepresent embodiment, the dimming layer 1 is doped with a specific elementsuch as hydrogen, whereby the state of the dimming layer 1 is changed.Therefore, by adopting the constitution in which two conversion layers 2a, 2 b sandwich the dimming layer 1, efficient doping becomes possible,whereby the speed of the state change necessary for dimming is improved.Since the dimming layer 1 can function as an electrode, the dimminglayer 1 is used as an electrode in the example of FIG. 12.

In the example of FIG. 12, the portion which performs hydrogenabsorption/release has a three-layer structure including the firstconversion layer 2 a, the dimming layer 1, and the second conversionlayer 2 b, but may have even more layers. Even if sufficient dimmingcannot be attained in the case where the dimming layer 1 is of a singlelayer, it would become possible to attain a sufficient dimming byincreasing the number of layers in the dimming layer 1.

Next, with reference to FIG. 13, another dimming device 10D will bedescribed.

In the dimming device 10D, the conversion layer 2 has a multi-layerstructure in order to separate the functions of the conversion layer 2.As described above, the functions of the conversion layer 2 are to storehydrogen, and to release/re-store hydrogen in accordance with chargeinjection/release. Rather than realizing these functions with a singlematerial, it would be easier to select a different material for eachfunction, and stack layers that are composed of the respectivematerials. In other words, by separating the conversion layer into afirst conversion layer 2 a composed of a charge transport material or anelectrolyte material for performing exchanges of charges or ions and asecond conversion layer 2 b formed from a material having a hydrogenstoring function, efficient hydrogen movement can be realized.

Herein, a charge ion exchange layer formed by mixing a conductivepolymer material P1 (a material capable of transporting both charges,i.e., electrons and holes) and an acrylic resin having about the samerefractive index as that of glass is used as the first conversion layer2 a. Moreover, a blended resin obtained by mixing ultrafine particles(dispersion center radius: 10 nm) of an Ni alloy, which is an AB5 typeMm hydrogen storage alloy, and an acrylic resin having about the samerefractive index as that of glass is used so as to function as thesecond conversion layer 2 b.

Hereinafter, specific embodiments of the display system according to thepresent invention will be described.

Embodiment 1

With reference to FIG. 14, a first embodiment of the display systemaccording to the present invention will be described.

As shown in FIG. 14, the display system 100A of the present embodimentcomprises: a liquid crystal display device 20; a backlight (illuminationdevice) 30 disposed on the rear face side (i.e., the opposite side fromthe viewer) of the liquid crystal display device 20; and a dimmingdevice 10 disposed between the liquid crystal display device 20 and thebacklight 30. Typically, a pair of polarizer plates 40 a and 40 b areprovided so as to sandwich the liquid crystal display device 20 and thedimming device 10.

The liquid crystal display device 20 comprises a pair of substrates 21and 22 and a liquid crystal layer 23 interposed therebetween. On thesurfaces of the pair of substrates 21 and 22 facing the liquid crystallayer 23, electrodes 24 and 25 for applying a voltage across the liquidcrystal layer 23 and alignment films 26 and 27 for aligning the liquidcrystal molecules in the liquid crystal layer 23 are provided. Therear-face-side substrate 21 is an active matrix substrate having a thinfilm transistor 28 (as a switching device) for each pixel.

The liquid crystal display device 20 has a substantially similarconstitution to that of a commonly-used transmission type liquid crystaldisplay device, and can be produced in a substantially similar manner.However, since the dimming device 10 is disposed at the rear face side,it is preferable that the rear-face-side substrate 21 is as thin aspossible, from the standpoints of securing light transmittance andreducing parallax. In the present embodiment, a glass substrate is usedas the rear-face-side substrate 21. By placing the liquid crystaldisplay device 20 into a glass etchant after the outer periphery thereofis firmly sealed, the thickness of the substrate 21 is set to 0.2 mm.

The dimming device 10 of the present embodiment has a layered structureincluding a dimming layer 1 and a conversion layer 2, such that thelight reflectance (optical characteristics) of the dimming layer 1changes in response to electrical stimulations. This dimming device 10comprises a pair of electrodes 3 a, 3 b sandwiching the dimming layer 1and the conversion layer 2, and further a substrate 4 supporting thelayered structure. Herein, the dimming device 10 is produced as follows.

First, a glass substrate is prepared as the substrate 4, and on itssurface, a transparent conductive film of ITO, having a thickness of 150nm, is formed by a sputter technique. Note that a plastic substrate maybe used as the substrate 4. Next, this transparent conductive film ispatterned into stripes with substantially the same pitch as a pixelpitch of the liquid crystal display device 20, thus forming theelectrodes 3 b.

Next, the conversion layer 2 is formed on the electrodes 3 b by using ablend of: ultrafine particles (dispersion center radius: 10 nm) of an Nialloy, which is an AB5 type Mm hydrogen storage alloy; a conductivepolymer material P1 (a material capable of transporting both charges,i.e., electrons and holes); and, as a binder resin, an acrylic resinhaving about the same refractive index as that of glass. Since thisblended resin can be made into a solution, a spin coating technique isused to form the conversion layer 2 so as to have a thickness of about500 nm. As for the hydrogen storage alloy, that which has hydrogenstored in advance is used.

Next, by vapor-depositing yttrium (Y) on the conversion layer 2, thedimming layer 1 having a thickness of 50 nm is formed. Thereafter, atransparent conductive film of ITO is formed on the dimming layer 1 by asputter technique. This transparent conductive film is patterned intostripes perpendicular to the electrodes 3 b, with substantially the samepitch as the pixel pitch of the liquid crystal display device 20, thusforming the electrodes 3 a. At each intersection between the stripe-likeelectrodes 3 a and electrodes 3 b, a dimming region is defined, eachdimming region corresponding to each pixel of the liquid crystal displaydevice 20.

The dimming device 10 and the liquid crystal display device 20 thusproduced are placed one on top of the other, in such a manner that thedimming regions overlap the pixels. These are sandwiched by thepolarizer plates 40 a, 40 b, and furthermore, the backlight 30 is placedat the rear face side of the dimming device 10, whereby the displaysystem 100A is obtained. As the backlight 30, an illumination deviceused for a commonly-used transmission type liquid crystal displayapparatus can be used.

The display system 100A is able to switch between the light transmittingstate and the light reflecting state of the dimming device 10 based onvoltage application, and allows the liquid crystal display device 20 tofunction as either a reflection type liquid crystal display device or atransmission type liquid crystal display device. As a result, an optimumdisplay mode can be selected in accordance with the intensity of ambientlight. Furthermore, in the display system 100A, switching of displaymodes is realized through switching of the dimming device 10. Thus,since each of the plurality of pixels of the liquid crystal displaydevice 20 does not need to be divided into a region for reflecting lightand a region for transmitting light, each entire pixel can contribute todisplaying either during display under the reflection mode or duringdisplay under the transmission mode. Therefore, as compared to aconventional liquid crystal display apparatus of atransmission/reflection dual-use type, a bright and high-contrast ratiodisplay can be realized in both the reflection mode and the transmissionmode. Therefore, the display system 100A can be suitably used in varioussituations, i.e., in a multitude of scenes.

Moreover, in the present embodiment, the electrodes 3 a, 3 b arepatterned into predetermined shapes, and the dimming device 10 includesa plurality of dimming regions each of which is independently able toswitchably present a light reflecting state or a light transmittingstate. Thus, when a plurality of types of information are displayed onthe liquid crystal display device 20, the light reflecting state orlight transmitting state of each dimming region can be selectivelyswitched in accordance with the type of information. Therefore, thedisplay system 100A is suitable for the displaying of multiple contents.

Note that, depending on the display device used, different controls maybe required for displaying under the reflection mode and displayingunder the transmission mode. Therefore, preferably, the display deviceis able to supply display signals of different types to a display regionin which display is performed by modulating light which has beentransmitted through the dimming device 10 and to a display region inwhich display is performed by modulating light which has been reflectedby the dimming device 10.

For example, in the case of the liquid crystal display device 20, lighttravels through the liquid crystal layer 23 twice under the reflectionmode, whereas light travels through the liquid crystal layer 23 onlyonce under the transmission mode. Therefore, between a pixel whichperforms display under the reflection mode and a pixel which performsdisplay under the transmission mode, the dynamic range is different evenwhen producing the same gray scale level, and the amplitude of anelectric signal to be supplied to the pixel is also different. Generallyspeaking, it is considered that the reflection mode is able to provide alarge change in light characteristics with a smaller range of control.

Therefore, two types of signals, i.e., one for the reflection mode andone for the transmission mode, may be provided for input to a driver forcontrolling the liquid crystal display device 20, and in accordance withthe switching of each dimming region of the dimming device 10, a displaysignal for the reflection mode or a display signal for the transmissionmode may be selectively supplied to each pixel of the liquid crystaldisplay device 20. As a result, displaying which is optimum with respectto the display mode can be performed in each pixel of the liquid crystaldisplay device 20, and displaying which provides a higher visualrecognition can be performed.

Embodiment 2

With reference to FIG. 15, a second embodiment of the display systemaccording to the present invention will be described.

A display system 100B of the present embodiment differs from the displaysystem 100A shown in FIG. 14 in that a dimming device 10 is placedinside a liquid crystal display device 20.

As shown in FIG. 15, in the display system 100B, the dimming device 10is built inside the liquid crystal display device 20. More specifically,when fabricating the rear-face-side active matrix substrate, a step ofproducing the dimming device 10 is introduced so as to provide thedimming device 10 upon a substrate 21.

For example, after forming TFTs 28 on the substrate 21, the dimmingdevice 10 is built in each pixel. The dimming device 10 can be producedin a similar manner to Embodiment 1. After producing the dimming device10, a planarization film (overcoat layer) 29 is formed so as to coverthe TFTs 28 and the dimming device 10. Then, pixel electrodes 24 formedon the planarization film 29 are electrically connected to the TFTs 28via throughholes 29 a, whereby an active matrix substrate is completed.Thereafter, similarly to the production steps of a commonly-used liquidcrystal display device, the active matrix substrate and a countersubstrate are attached together, and a liquid crystal material to becomea liquid crystal layer 23 is injected, whereby the liquid crystaldisplay device 20 having the dimming device 10 internalized therein iscompleted.

The display system 100B of the present embodiment is also able toperform displaying under either the reflection mode or the transmissionmode by switching between the light reflecting state and the lighttransmitting state of the dimming device 10, and therefore is suitablyemployed for use in a multitude of scenes and displaying of multiplecontents, similarly to the display system 100A shown in FIG. 14.

Furthermore, according to the present embodiment, the dimming device 10is disposed inside the liquid crystal display device 20, so that theentire display system can be made thinner and lighter-weight. Moreover,since the dimming device 10 is disposed inside the liquid crystaldisplay device 20, parallax can be reduced, whereby display quality canbe further improved. In the example shown in FIG. 15, the substrate 21is not present between the dimming device 10 and the liquid crystaldisplay device 20, and therefore parallax is reduced correspondingly.

Embodiment 3

With reference to FIG. 16, FIG. 17, and FIG. 18, third embodiments ofthe display system according to the present invention will be described.

Display systems 100C, 100D, and 100E according to the present embodimenteach include color filters, and therefore are capable of performingcolor display. As the dimming device 10 and the liquid crystal displaydevice 20 of the display systems 100C, 100D, and 100E, those similar totheir counterparts in the display systems 100A and 100B shown in FIG. 14and FIG. 15 can be used.

In the display system 100C shown in FIG. 16, the liquid crystal displaydevice 20 includes color filters 50. Specifically, the color filters 50are formed on the surface of the front-face-side substrate 22 facing theliquid crystal layer 23.

On the other hand, in the display system 100D shown in FIG. 17, thedimming device 10 includes color filters 50. Specifically, the colorfilters 50 are formed on front-face-side electrodes 3 a.

In the display system 100E shown in FIG. 18, both the liquid crystaldisplay device 20 and the dimming device 10 include color filters 50,the color filters 50 being formed on a front-face-side substrate 21 ofthe liquid crystal display device 20 and front-face-side electrodes 3 aof the dimming device 10.

Although differing in the positioning of color filters, theaforementioned display systems 100C, 100D, and 100E are all able toperform color display. In the display system 100E shown in FIG. 18,since both the dimming device 10 and the liquid crystal display device20 include color filters 50, great coloring effects are provided by thecolor filters, so that displaying can be performed with good colorpurity.

Embodiment 4

With reference to FIG. 19, a fourth embodiment of the display systemaccording to the present invention will be described.

In the display system 100F of the present embodiment, both a liquidcrystal display device 20 and a dimming device 10 include color filters.However, in the display system 100E shown in FIG. 18, color filters 50are formed on front-face-side electrodes 3 a. On the other hand, in thepresent embodiment, a conversion layer 2′ of the dimming device 10 alsofunctions as color filters. The conversion layer 2′ functioning as colorfilters is disposed on the opposite side from the viewer with respect tothe dimming layer 1.

The conversion layer 2′ functioning also as color filters can be formedby, for example, mixing coloring pigments of RGB in the transparentconversion layer described in Embodiment 1. The conversion layermaterial in which coloring pigments of RGB are mixed can be made into asolution, and therefore an ink jet technique can be used to form theconversion layer 2′ in accordance with the pixel pattern. It will beappreciated that, without being limited to an ink jet technique, ascreen printing technique or a rolling press technique can also be usedfor the formation.

According to the present embodiment, the color filters 50 are providedon the liquid crystal display device 20, while the conversion layer 2′on the rear face side of the dimming layer 1 also functions as colorfilters. As a result, as shown in FIG. 19, light travels through thecolor filters twice (i.e., once through the color filters 50 and oncethrough the conversion layer 2′) when performing display under thetransmission mode, and travels through the color filters also twice(i.e., twice through the color filters 50) when performing display underthe reflection mode. In other words, the number of times that lighttravels through the color filters is the same between the reflectionmode and the transmission mode. Therefore, similar colorations can beobtained between displaying under the reflection mode and displayingunder the transmission mode, thus further improving the display quality.

On the other hand, in the display systems 100C, 100D, and 100E shown inFIG. 16, FIG. 17, and FIG. 18, the number of times that light travelsthrough the color filters differs between the reflection mode and thetransmission mode, such that the number of times that light travelsthrough the color filters is twice as large under the reflection mode asunder the transmission mode. Therefore, if the colors of the colorfilters are prescribed so that optimum coloration will be obtained underthe transmission mode, the display will be dark under the reflectionmode. Conversely, if the colors of the color filters are prescribed sothat optimum coloration will be obtained under the reflection mode, thenthe colors will become weak under the transmission mode.

In the display system 100F, during display under the reflection mode,light travels twice through only the color filters 50 of the liquidcrystal display device 20. Therefore, coloration under the reflectionmode can be optimized by adjusting the colors of the color filters 50.On the other hand, during display under the transmission mode, lighttravels once through the color filters 50 of the liquid crystal displaydevice 20 and once through the color filters (conversion layer 2′) ofthe dimming device 10. Therefore, by adjusting the colors of theconversion layer 2′ while prescribing the color filters 50 so thatoptimum coloration will be obtained under the reflection mode, thecoloration under the transmission mode can also be optimized.

(Other Dimming Devices)

In the above description, a dimming device having as a dimming layer athin film containing a dimming material was illustrated. However, adimming device of a type in which a dimming material is made intoparticle can also be used.

With reference to FIG. 20, the fundamental constitution of this type ofdimming device will be described. As shown in FIG. 20, this dimmingdevice has a layered structure including a dimming layer M1 and aconversion layer M2, such that the light reflectance of the dimminglayer M1 changes in response to external stimulations.

The dimming layer M1 contains particles m1 (which may hereinafter bereferred to as “dimming particles”) of a dimming material whose opticalcharacteristics change in accordance with the concentration of aspecific element. Preferable examples of the dimming material are Y, La,and Mg₂Ni alloy as described above. Materials such as Y, La, and Mg₂Nalloy undergo transitions between metal and semiconductor (or insulator)states in accordance with hydrogen concentration. The dimming layer M1contains a binder resin, for example, and the aforementioned dimmingparticles m1 are dispersed within the binder resin. Moreover, thedimming layer M1 contains an electrolytic material (e.g., a conductivepolymer) for transporting hydrogen ions or hydrogen from the conversionlayer M2.

The conversion layer M2 contains a conversion material capable ofcontaining a specific element such as hydrogen. The conversion materialreleases or absorbs the aforementioned specific element (e.g., hydrogen)in accordance with an external stimulation, such as a charge (electronsor holes) injection/release or light irradiation.

This dimming device is also capable of switching between a reflectionstate and a transparent state, based on the same mechanism as that ofthe dimming device shown in FIG. 5. However, although the dimming layerM1 contains the dimming particles m1 and each dimming particle m1mirror-reflects light while in a metallic state, the reflectingdirection is random, so that the dimming layer M1 as a wholediffuse-reflects the light. As a result, white reflected light isobtained.

The following advantages are obtained by making the dimming materialinto particles. The surface area of the dimming material can be madegreater than in the case of using a thin film of dimming material as thedimming layer. Therefore, the reaction efficiency between the dimmingmaterial and hydrogen is improved, and a rapider switching becomespossible. Since the state of the dimming material contained in thedimming layer can be more surely controlled, the difference inreflectance between a diffuse-reflection state and a transparent stateof the dimming layer can be enlarged. As a result, by using this dimmingdevice for a display system, a clearer display is obtained. Furthermore,since light entering the dimming layer is diffuse-reflected in thisdimming device, it can be applied to a display system with a particularadvantage.

In order for the dimming particles m1 to reflect light, it is desirablethat each dimming particle m1 has a grain size greater than the visiblelight wavelength. Therefore, the dimming particles m1 preferably have agrain size of 350 nm or more, and more preferably 800 nm or more. If itis 800 nm or more, transmission of visible light through the dimmingparticles m1 can be more surely prevented, so that the light reflectanceof the dimming layer M1 can be enhanced. On the other hand, the grainsize of the dimming particles m1 is preferably smaller than thethickness of the dimming layer M1. If the grain size is greater than thethickness of the dimming layer M1, the aforementioned advantageassociated with making the dimming material into particles cannot beobtained. More preferably, the grain size of the dimming particles m1 is30 μm or less. Still more preferably, the grain size is 3 μm or less.When the grain size of the dimming material is 1 μm, for example, thedimming layer M1 preferably has a thickness of about 3 μm.

The dimming device having the structure shown in FIG. 20 utilizes amechanism in which hydrogen ions move between the dimming layer M1 andthe conversion layer M2 responsive to charge injection/release as shownin FIGS. 6(a) to (c), but a different mechanism may be adopted. Forexample, a mechanism where hydrogen ions move between the conversionlayer M2 and the dimming layer M1 via electrochemical reactions may beutilized. In this case, the binder resin contained in the dimming layerM1 may be used as a solid electrolyte, or a layer of solid electrolytemay further be provided between the dimming layer M1 and the conversionlayer M2. In this case, the conversion material contained in theconversion layer M2 does not need to be a material which stores orreleases hydrogen, but may be a material which undergoes a reaction ofcounterions so as to correspond to the hydrogen ion reaction occurringin the dimming material.

Alternatively, the conversion layer M2 may not be comprised. In thiscase, a mechanism where hydrogen ions move between the dimming layer M1and the atmosphere in accordance with the hydrogen pressure in theatmosphere may be utilized. Alternatively, the dimming layer M1 mayfurther contain a conversion material, and hydrogen ions may be movedbetween the dimming particles m1 and the conversion material inside thedimming layer M1.

Regardless of which mechanism is utilized, the optical characteristicsof the dimming layer M1 change in accordance with the hydrogen ionconcentration, as shown in FIG. 20.

Note that, among the above, it is preferable to utilize the mechanism inwhich hydrogen ions are moved based on charge injection/release. In thecase where hydrogen is driven by causing the hydrogen equilibrium stateto be changed based on movements of charges (electrons or holes), it isunnecessary to involve any ions other than hydrogen ions in thereaction. This leads to an advantage in that the response speed ishigher than in the case where a mechanism based on an electrochemicalreaction involving a plurality of kinds of ions is utilized. Moreover,since no electrochemical reaction occurs, there is little possibilityfor hydrogen gas to be generated at the positive side, so that a stableoperation is enabled as an electronic device.

Hereinafter, a more specifically constitution of a dimming devicecontaining dimming particles m1 will be described.

The dimming device 10E shown in FIG. 21 has a layered structureincluding a dimming layer 1 and a conversion layer 2. This layeredstructure is substantially the same as the structure shown in FIG. 20.The light reflectance (optical characteristics) of the dimming layer 1changes in response to electrical stimulations. This dimming device 10Ecomprises a pair of electrodes 3 a, 3 b sandwiching the dimming layer 1and the conversion layer 2, and a substrate 4 supporting the layeredstructure. An appropriate voltage is to be externally applied to thepair of electrodes 3 a, 3 b. However, the electrode 3 a and theelectrode 3 b may simply be short-circuited as necessary.

Note that the layering order of the conversion layer 2 and the dimminglayer 1 with respect to the substrate 4 is not limited to that which isillustrated in the figures, but the conversion layer 2 may be disposedso as to be closer to the substrate 4, with the dimming layer 1 beingformed thereupon.

In the dimming layer 10E, microparticles (e.g., yttrium or lanthanum,hereinafter referred to as “dimming microparticles”) which have beenformed by using a dimming material whose optical characteristics changein accordance with hydrogen concentration are dispersed in a binderresin.

The conversion layer 2 contains a conversion material which is capableof containing hydrogen. This conversion material performs exchanges ofelectrons with the electrode 3 a, thus effecting release/absorption ofhydrogen ions (H+).

In the illustrated example, a positive potential is applied to theelectrode 3 a and a negative potential is applied to the electrode 3 b,whereby hydrogen ions are released from the conversion material in theconversion layer 2 containing a sufficient amount of hydrogen inadvance. The released hydrogen ions move within an electric field whichis generated in the layered structure, and reach the dimming layer 1,thus leaving the dimming microparticles doped therewith. Such amechanism of hydrogen release and movement is as described above. Thedimming material of the dimming microparticles binds to hydrogen, thusforming a hydrogen metal compound. As a result, the dimmingmicroparticles, which were initially in a metallic state, change to asemiconductor or insulator that transmits visible light.

The average grain size of the dimming microparticles contained in thedimming layer 1 is 1 μm, for example. The dimming microparticles aretypically dispersed in a binder resin. As a binder resin, an acrylicresin having about the same refractive index as that of glass is used.Moreover, the dimming layer 1 further contains an electricallyconductive material for performing exchanges of hydrogen ions and chargebetween the dimming microparticles and the conversion layer 2. As theelectrically conductive material, a material capable of iontransmission, such as a liquid or solid electrolyte, or a conductivepolymer (e.g., P2) or a charge transfer complex which transmits charge(electrons or holes) can be used.

The dimming layer 1 can be formed by preparing an application solutionby dispersing the aforementioned dimming microparticles in a solution ofbinder resin, and further dissolving an electrically conductive materialtherein, and thereafter applying the application solution onto theelectrode 3 b by a spin coating technique, for example. The thickness ofthe dimming layer 1 is about 3 μm, for example. The formation of thedimming layer 1 may be performed by an ink jet technique or any otherthin film deposition technique. The light incident-side face of thedimming layer 1 may be flat, or have bumps and dents. A dimming layer 1having bumps and dents can be formed by using a substrate 4 or electrode3 b having bumps and dents and applying the aforementioned applicationsolution onto the under layer having bumps and dents, for example.

The preferable thickness of the dimming layer 1 is no less than 1.5 μmand no more than 50 μm. If it is less than 1.5 μm, it may be impossibleto obtain a dimming layer 1 having a high reflectance, or the grain sizeof the dimming microparticles used in the dimming layer 1 may belimited. On the other hand, if it is greater than 50 μm, theconductivity of the dimming layer 1 may be lowered.

The conversion material contained in the conversion layer 2 is able tostore and retain atoms or ions of hydrogen in its stationary state, andchanges its hydrogen storage amount (retained amount) in accordance withexternal stimulations. As this material capable of storing hydrogen,alloys such as LaNi₅, MnNi₅, CaNi₅, TiMn_(1.5), ZrMn_(1.5), ZrMn₂, TiNi,TiFe, and Mg₂Ni can be used. Moreover, carbon nanotubes (CNT) may alsobe used.

The conversion layer 2 may contain an electrically conductive materialin addition to the hydrogen storage material. If an electricallyconductive material is contained in the conversion layer 2, it ispossible to rapidly perform exchanges of hydrogen ions with the dimminglayer 1. As an electrically conductive material, a material capable ofion transmission, such as a liquid or solid electrolyte, or a conductivepolymer or a charge transfer complex which transmits charge (electronsor holes) can be used. Moreover, in addition to the aforementionedhydrogen storage material or electrically conductive material, a bindingmaterial such as a binder resin may be added to the conversion layer 2as necessary. Note that, in order to surely restrain the charge whichhas been injected from one electrode from immediately moving to theother electrode, a separator layer may be inserted between the dimminglayer and the conversion layer. As the material of the separator layer,it is desirable to choose a material which permits ion movement but isunlikely to permit charge movement. For example, an ion exchanger, aporous insulator, an ion conductive polymer material or the like can beused. By disposing a separate layer composed of such a material, thecharge which has been injected from an electrode is surely preventedfrom penetrating to the other electrode, whereby the charge movementefficiency between the dimming layer and the conversion layer can beenhanced.

In the case where the conversion layer 2 is composed of a mixture of aplurality of materials, a solution obtained by dissolving such materialsin a solvent may be prepared and applied by a spin coating technique ora printing technique, whereby the conversion layer 2 can be easilyformed. Such formation of the conversion layer 2 may be performed by anink jet technique or any other thin film deposition technique.

As described above, in the dimming device 10E, exchanges of charges andions occur inside the conversion layer 2 responsive to application of avoltage to the electrodes 3 a, 3 b. As a result, owing to theaforementioned mechanism, hydrogen movement can be induced between theconversion layer 2 and the dimming microparticles. Therefore, forexample, by using a dimming layer 1 which is undoped with hydrogen in aninitial state and a conversion layer 2 having hydrogen stored inadvance, if a voltage as shown in FIG. 20 is applied, hydrogen ions movefrom the positive side to the negative side, thus making the dimmingmicroparticles doped therewith. In other words, a hydrogen releasereaction progresses at the positive side, whereas a combination reactionbetween hydrogen and a metal progresses at the negative side, whereby ahydrogen metal compound is formed. On the other hand, if a voltage inthe opposite direction is applied, a hydrogen movement in the oppositedirection occurs. Therefore, by reversing the polarity of the appliedvoltage, the optical state of the dimming layer 1 can be reversiblyswitched between metallic luster and transparent.

When only contemplating a movement of the hydrogen stored in theconversion layer 2, the electrodes 3 a and the electrodes 3 b might beshort-circuited outside of the layered structure. Such short-circuitingwould be a similar phenomenon to a discharging of a secondary battery,and enable restoration of the internal state of the layered structure tothe initial state.

Since the conversion layer 2 and the dimming layer 1 have the ability toretain hydrogen, when voltage application is not performed (when theexternal circuit is open), no hydrogen movement occurs, so that theoptical state of the dimming layer 1 is retained (memory function of thedimming layer). Therefore, by choosing a material having a good hydrogenretaining ability, it becomes possible to retain a dimmed state for along period of time without consuming power.

Contrary to the above example, a dimming layer 1 doped with hydrogen inadvance, and a conversion layer 2 in a state not storing hydrogen may beused. In that case, hydrogen may be moved from the dimming layer 1 tothe conversion layer 2 by applying a positive potential to the dimminglayer 1 and a negative potential to the conversion layer 2, thus causinga change in the optical state of the dimming material in the dimminglayer 1.

In the dimming device 10E, the light reflectance/light transmittance ofdimming microparticles can be controlled based on a doping amount ofhydrogen. Therefore, by controlling the voltage to be applied to theelectrode and application time (e.g., a duty ratio), the lightreflectance/light transmittance of the dimming layer 1 can becontrolled. By utilizing the memory ability based on hydrogen retainingability, an appropriate light reflectance/light transmittance can beeasily retained.

In appropriately controlling such hydrogen storage/release, it isnecessary to pay attention to the hydrogen equilibriumpressure-composition isotherm (PTC characteristic curve), as has beendescribed with reference to FIG. 8 regarding the dimming device 10 shownin FIG. 7.

In the dimming device 10E, too, it is preferable to perform switchingoperations in the plateau region of the PTC characteristic curve.Moreover, it is desirable that the conversion layer 2 and the dimminglayer 1 exhibit substantially similar PTC characteristics. Morespecifically, as shown in FIG. 8, it is desirable that the ranges of“hydrogen storage amount” of the plateau regions of the PTCcharacteristic curves of the conversion layer 2 and the dimming layer 1overlap each other, and that the “hydrogen equilibrium pressure” levelsare substantially equal. Moreover, it is more preferable that thehydrogen storage amount range (span) of the plateau region of the PTCcharacteristic curve of the conversion layer 2 is of a size encompassingthe hydrogen storage amount range (span) of the plateau region of thePTC characteristic curve of the dimming layer 1.

FIG. 21 is referred to again. Since the dimming device 10E shown in FIG.21 performs switching between a metal diffuse reflection state and atransparent state, it is preferable that the entire device has a hightransparency. In order to establish a high transparency state, not onlythe substrate 4 and the electrodes 3 a, 3 b but also the conversionlayer 2 must be formed from a material which has a high transmittance(no absorption) in the entire visible light region. However, aconversion material such as a hydrogen storage material is often a metalor a colored material, and it is difficult to form a conversion layer 2having a high transparence from a layer of such a conversion material.Therefore, it is preferable to form the conversion layer 2 by mixingmicroparticles of a conversion material with a transparent material.Specifically, nanoparticles having a grain size equal to or less thanthe light wavelength are formed from a conversion material, and thesenanoparticles may be bound with a binder resin which has a goodtransparence. A conversion layer 2 thus produced is not only able toexhibit both transparence and hydrogen storing ability, but an increasein the hydrogen absorption/release efficiency can also be expected sincethe conversion material has an increased surface area because of beingmade into nanoparticles. An increase in the hydrogen absorption/releaseefficiency of the conversion material is preferable because the responsespeed of the dimming operation would be improved. As a conversionmaterial in an ultrafine particle state, a carbon type material (e.g.,CNT and fullerene), a potassium-graphite interlayer compound or the likecan also be used.

In order to realize exchanges of charges and ions between the dimminglayer 1 and the conversion layer 2, it is preferable to dispose a filmof conductive polymer P1 between the dimming layer 1 and the conversionlayer 2. In addition to a polymer film having a charge moving ability,an electrolyte film may be disposed. By disposing such a film, movementof hydrogen ions becomes likely to occur via the electrolyte, andtherefore it is possible to improve the characteristics.

Hereinafter, with reference to FIG. 22 and FIG. 23, other dimmingdevices 10F, 10G, and 10H of the type containing dimming particles willbe described.

The dimming device 10F of FIG. 22(a) has a constitution in which aconversion layer is separated into a plurality of layers, i.e., a firstconversion layer 2 a and a second conversion layer 2 b. In thehitherto-described dimming devices, the dimming layer 1 is doped with aspecific element such as hydrogen, whereby the state of the dimminglayer 1 is changed. Therefore, by adopting the constitution in which twoconversion layers 2 a, 2 b sandwich the dimming layer 1, efficientdoping becomes possible, whereby the speed of the state change necessaryfor dimming is improved. Since the dimming layer 1 can function as anelectrode, the dimming layer 1 is used as an electrode in the example ofFIG. 22(a).

In the dimming device of FIG. 22(a), the portion which performs hydrogenabsorption/release has a three-layer structure including the firstconversion layer 2 a, the dimming layer 1, and the second conversionlayer 2 b, but may have even more layers. Even if sufficient dimmingcannot be attained in the case where the dimming layer 1 is of a singlelayer, it would become possible to attain a sufficient dimming byincreasing the number of layers in the dimming layer 1.

In the case where the dimming layer 1 has such a low conductivity thatit cannot be used as an electrode, as in a dimming device 10G shown inFIG. 22(b), the dimming layer may be separated into two layers, i.e., afirst dimming layer 1 a and a second dimming layer 1 b, and an electrode3 c may be inserted between these dimming layers. In the dimming device10G of FIG. 22(b), too, the dimming layer 1 may have even more layers.

The dimming device of either FIG. 22(a) or (b) can be easily produced bysequentially stacking the respective layers. Note that the dimminglayer, the conversion layer, the electrodes, and the substrate may havesimilar constitutions to that of dimming device 10E shown in FIG. 21except that the number of stacked layers may be different.

In the dimming device 10H shown in FIG. 23, the conversion layer 2 has amulti-layer structure in order to separate the functions of theconversion layer 2. As described above, the functions of the conversionlayer 2 are to store hydrogen, and to release/re-store hydrogen inaccordance with charge injection/release. Rather than realizing thesefunctions with a single material, it would be easier to select adifferent material for each function, and stack layers that are composedof the respective materials. In other words, by separating theconversion layer into a first conversion layer 2 a composed of a chargetransport material or an electrolyte material for performing exchangesof charges or ions and a first conversion layer 2 a formed from amaterial having a hydrogen storing function, efficient hydrogen movementcan be realized.

Herein, a charge ion exchange layer formed by mixing a conductivepolymer material P1 (a material capable of transporting both charges,i.e., electrons and holes) and an acrylic resin having about the samerefractive index as that of glass is used as the first conversion layer2 a. Moreover, a blended resin obtained by mixing ultrafine particles(dispersion center radius: 10 nm) of an Ni alloy, which is an AB5 typeMm hydrogen storage alloy, and an acrylic resin having about the samerefractive index as that of glass is used so as to function as thesecond conversion layer 2 b. Note that such separation of functions ofthe conversion layers can also be applied to any of the dimming devicesshown in FIG. 21 and FIG. 22.

As the dimming device to be used in a display system according to thepresent invention, any dimming device that is capable of switchablypresenting a light reflecting state or a light transmitting state can beused, without being limited to those exemplified here. For example, aliquid crystal device comprising a liquid crystal layer composed of acholesteric liquid crystal material, or a liquid crystal devicecomprising a liquid crystal layer of a polymer dispersed type may beused as the dimming device. In the cases where such a liquid crystaldevice is used as the dimming device, too, since the dimming deviceincludes dimming regions and is constructed so as to be able toselectively switch between a light reflecting state and a lighttransmitting state of each dimming region in accordance with the type ofinformation displayed on the display device, it is possible to performdisplay in a mode which provides optimum visual recognition depending oneach content type. Therefore, the display system can be suitably usedfor displaying multiple contents.

However, note that those dimming devices which have been described withreference to the figures, which are capable of switching between ametallic reflection state and a transmitting state, are able to providea high efficiency of light utility (reflectance) because of utilizing ametallic reflection state, and are able to reduce power consumptionbecause of having a memory ability. Therefore, by using such a dimmingdevice, a display system which is particularly suitable for use in amultitude of scenes can be obtained.

On the other hand, by principle, a liquid crystal device usingcholesteric liquid crystal can only reflect half of the incident light(either the p wave or the s wave), and reflected light will exist evenin a transmitting state, thus resulting in a low efficiency of lightutility. A liquid crystal device using a polymer dispersed type liquidcrystal does not have a memory ability, and therefore a voltage mustalways be applied across the liquid crystal layer, thus beingdisadvantageous in terms of power consumption; and the liquid crystalmaterial in spherical shapes dispersed in the polymer matrix willreflect light under total reflection conditions based on a refractiveindex difference with respect to the matrix material, and it istherefore impossible to reflect light in all directions. A dimmingdevice utilizing a metallic reflection state is basically able toreflect light from all directions, and therefore has a high efficiencyof light utility.

By disposing a dimming device which is able to mirror-reflect light(e.g., that shown in FIG. 7, for example) on the front face of a displaydevice, it becomes possible to use the display system as a piece ofinterior equipment which serves both as a display and a mirror.

According to the present invention, there is provided a display systemwhich has good display characteristics during both display under thetransmission mode and display under the reflection mode, and which issuitable for use in a multitude of scenes and/or displaying of multiplecontents.

1-48. (canceled)
 49. A display system comprising: a dimming devicecapable of switchably presenting a light reflecting state or a lighttransmitting state; and a display device for displaying information bymodulating light transmitted through the dimming device and/or lightreflected by the dimming device, wherein the dimming device has aplurality of regions each being independently capable of switchablypresenting a light reflecting state or a light transmitting state, and,when a plurality of types of information are being displayed on thedisplay device, the dimming device is capable of selectively switchingbetween the light reflecting state or the light transmitting state ofeach of the plurality of regions in accordance with the types ofinformation being displayed.
 50. The display system of claim 49, whereinthe display device supplies a display signal to a first display regionfor performing display by modulating the light transmitted through thedimming device, and supplies a display signal to a second display regionfor performing display by modulating the light reflected by the dimmingdevice, the display signals being of different types.
 51. The displaysystem of claim 49, wherein, the display device has a plurality ofpixels; and each of the plurality of regions of the dimming devicecorresponds to each of the plurality of pixels in a one-to-onerelationship.
 52. The display system of claim 49, wherein, the dimmingdevice is a dimming device having a layered structure including a firstlayer and a second layer, such that a light reflectance of the firstlayer changes in response to an external stimulation; the first layercontains a first material whose optical characteristics change inaccordance with a concentration of a specific element; and the secondlayer contains a second material capable of containing the specificelement, the second material releasing or absorbing the specific elementin accordance with the external stimulation.
 53. The display system ofclaim 49, wherein, the dimming device is a dimming device comprising adimming layer whose light reflectance changes in response to an externalstimulation; and the dimming layer contains a first material whoseoptical characteristics change in accordance with a concentration of aspecific element, the first material being particles.
 54. A displaysystem comprising: a dimming device capable of switchably presenting alight reflecting state or a light transmitting state; and a displaydevice for performing display by modulating incident light, wherein, thedimming device is a dimming device having a layered structure includinga first layer and a second layer, such that a light reflectance of thefirst layer changes in response to an external stimulation; the firstlayer contains a first material whose optical characteristics change inaccordance with a concentration of a specific element; and the secondlayer contains a second material capable of containing the specificelement, the second material releasing or absorbing the specific elementin accordance with the external stimulation.
 55. The display system ofclaim 54, wherein the display device performs display by modulatinglight transmitted through the dimming device and/or light reflected bythe dimming device.
 56. The display system of claim 54, wherein theelement is hydrogen, and the first material is able to transitionbetween a light reflecting state and a light transmitting state inaccordance with a hydrogen concentration.
 57. The display system ofclaim 56, wherein the second layer contains a hydrogen storage material.58. The display system of claim 57 operating in a region whererespective hydrogen equilibrium pressure-composition isotherms (PTCcharacteristic curves) of the first layer and the second layer aresubstantially flat.
 59. The display system of claim 58, wherein, in theregion where the PTC characteristic curves are substantially flat,hydrogen equilibrium pressures of the first layer and the second layerare about the same.
 60. The display system of claim 59, wherein a rangeof hydrogen storage amount of the second layer in the region where thePTC characteristic curve is substantially flat encompasses a range ofhydrogen storage amount of the first layer in the region where the PTCcharacteristic curve is substantially flat.
 61. The display system ofclaim 54, wherein the second material releases or absorbs the specificelement through exchanges of electrons.
 62. The display system of claim54, wherein the second material releases or absorbs the specific elementin response to light irradiation.
 63. The display system of claim 62,wherein the second layer contains a material having a photocatalyticability.
 64. The display system of claim 54, comprising a pair ofconductive layers for forming an electric field for causing ions of thespecific element to move from the second material to the first material,or from the first material to the second material.
 65. The displaysystem of claim 64, wherein the first and second layer are positionedbetween the pair of conductive layers.
 66. The display system of claim64, wherein the first layer has conductivity, and functions as one ofthe pair of conductive layers.
 67. The display system of claim 64,wherein the second layer has conductivity, and functions as one of thepair of conductive layers.
 68. The display system of claim 54, whereinthe second layer has a light transmitting ability.
 69. The displaysystem of claim 54, wherein at least one of the first layer and thesecond layer has a multi-layer structure.
 70. A display systemcomprising: a dimming device capable of switchably presenting a lightreflecting state or a light transmitting state; and a display device forperforming display by modulating incident light, wherein, the dimmingdevice is a dimming device comprising a dimming layer whose lightreflectance changes in response to an external stimulation; and thedimming layer contains a first material whose optical characteristicschange in accordance with a concentration of a specific element, thefirst material being particles.
 71. The display system of claim 70,wherein the display device performs display by modulating lighttransmitted through the dimming device and/or light reflected by thedimming device.
 72. The display system of claim 70, wherein the firstmaterial is able to transition between a light reflecting state and alight transmitting state in accordance with the concentration of thespecific element.
 73. The display system of claim 72, wherein thedimming layer diffuse-reflects light when the first material is in thelight reflecting state.
 74. The display system of claim 70, wherein adiameter of the particles is equal to or greater than 350 nm and equalto or less than a thickness of the dimming layer.
 75. The display systemof claim 70, wherein the specific element is hydrogen.
 76. The displaysystem of claim 70, further comprising a conversion layer containing asecond material capable of containing the specific element, wherein thesecond material releases or absorbs the specific element in accordancewith the external stimulation.
 77. The display system of claim 76,wherein the specific element is hydrogen, and the conversion layercontains a hydrogen storage material.
 78. The display system of claim 77operating in a region where respective hydrogen equilibriumpressure-composition isotherms (PTC characteristic curves) of thedimming layer and the conversion layer are substantially flat.
 79. Thedisplay system of claim 78, wherein, in the region where the PTCcharacteristic curves are substantially flat, hydrogen equilibriumpressures of the dimming layer and the conversion layer are about thesame.
 80. The display system of claim 79, wherein a range of hydrogenstorage amount of the conversion layer in the region where the PTCcharacteristic curve is substantially flat encompasses a range ofhydrogen storage amount of the dimming layer in the region where the PTCcharacteristic curve is substantially flat.
 81. The display system ofclaim 70, wherein the second material releases or absorbs the specificelement through exchanges of electrons.
 82. The display system of claim70, wherein the second material releases or absorbs the specific elementthrough an electrochemical reaction.
 83. The display system of claim 70,comprising a pair of conductive layers for forming an electric field forcausing ions of the specific element to move from the second material tothe first material, or from the first material to the second material.84. The display system of claim 83, wherein the dimming layer and theconversion layer are positioned between the pair of conductive layers.85. The display system of claim 83, wherein the dimming layer hasconductivity, and functions as one of the pair of conductive layers. 86.The display system of claim 83, wherein the conversion layer hasconductivity, and functions as one of the pair of conductive layers. 87.The display system of claim 70, wherein the conversion layer has a lighttransmitting ability.
 88. The display system of claim 70, wherein atleast one of the dimming layer and the conversion layer has amulti-layer structure.
 89. The display system of claim 49, wherein thedisplay device is a liquid crystal display device including a pair ofsubstrates and a liquid crystal layer provided between the pair ofsubstrates.
 90. The display system of claim 49, further comprising anillumination device disposed on an opposite side from a viewer withrespect to the display device.
 91. The display system of claim 90,wherein the dimming device is disposed between the display device andthe illumination device.
 92. The display system of claim 49, wherein thedimming device is disposed inside the display device.
 93. The displaysystem of claim 49, wherein the display device includes a first colorfilter.
 94. The display system of claim 49, wherein the dimming deviceincludes a second color filter.
 95. The display system of claim 54,wherein the display device includes a first color filter; the dimmingdevice includes a second color filter; and the second color filter isdisposed on an opposite side from a viewer with respect to the firstlayer.
 96. The display system of claim 70, wherein the display deviceincludes a first color filter; the dimming device includes a secondcolor filter; and the second color filter is disposed on an oppositeside from a viewer with respect to the dimming layer.